1. Field of the Invention
The technical field relates to a touch sensor. In addition, the technical field relates to a touch panel, a display portion of which includes a touch sensor, and a display device including a touch panel.
2. Description of the Related Art
In recent years, the market of liquid crystal displays and electroluminescence (EL) displays has grown, and the importance of the added value of panels has been increasing. Above all, touch panels with display portions including touch sensors have attracted attention as user interfaces and have been introduced into mobile devices such as portable game machines.
Further, it is proposed that personal authentication is performed with a touch sensor provided in a device which does not necessarily have a display portion, such as a fingerprint authentication device.
For example, a touch panel which can receive information by detecting light reaching a display screen with a photosensor provided in a pixel of a display portion has been developed (e.g., Patent Document 1).
In the touch panel including such kind of photosensor, the following techniques are proposed: a technique in which a change in amount of light by shadow of a finger, an object, or the like projected on a display screen is detected with a photo diode provided in a pixel as a photosensor for example; and a technique in which a change in amount of light caused by light from a light-emitting object such as a light pen is detected with a photo diode provided in a pixel as a photosensor for example.
[Reference]
    [Patent Document 1] Japanese Published Patent Application No. 2004-318819